An outdoor wedding reception is being linked to 11 confirmed cases in western Thessaloniki, in northern Greece.
The wedding was held on July 25 in the suburb of Ambelokipoi.
More than 150 people attended the wedding.
Officials are waiting for the results of 60 tests.
Three patients have been admitted to Papanikolaou hospital.
Meanwhile, Greece reported 78 new coronavirus cases in the latest 24-hour reporting period.
From today, Greece has made face masks compulsory in all indoor public places.
They were already obligatory on public transport, supermarkets, and Shops providing goods and services of all kind etc., but the government has now brought in stricter measures to try to fight a growing number of clusters of covid-19 cases in the country.
Personal responsibility “was and is the secret success of Greece,” Civil Protection Deputy Minister for Crisis Management Nikos Hardalias said, “and at this stage we must all exhibit the same sense responsibility and awareness.”